05000454/LER-2012-002
| Byron Station, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4542012002R02 - NRC Website | |
Background
The Containment Cooling System (VP) [BK] consists of two trains. Each VP train consists of two Reactor Containment Fan Coolers (RCFCs). Specifically, Train A of VP System consists of the A and C RCFCs and Train B consists of B and D RCFCs. There are two sets of cooling coils in each RCFC; One set of coils receive cooling water from the non safety-related Chilled Water (WO) [KM] System and the second set of coils receives cooling water from the safety-related Essential Service Water (SX) [BI] System. Upon receipt of an engineered safeguard signal, SX to the WO condensers is isolated and WO cooling is lost. The RCFCs only receive their cooling water from the SX system, accordingly.
A. Plant Operating Conditions Before the Event:
Unit 1 was in Mode 1 — Power Operations at approximately 100% power.
Reactor Coolant System (RC) [AB] was at normal operating temperature and pressure. No structures, systems, or components were inoperable at the start of this event that contributed to the event.
B. Description of Event
On March 29, 2012, an inspection was in progress for a water leak inside containment that was causing elevated containment sump levels. Part of this inspection involved looking for possible leakage coming from the SX coils within the RCFC's plenums. To accomplish this, each RCFC plenum access panel needed to be removed in order to access the SX coils section for inspection. At 1217 hours0.0141 days <br />0.338 hours <br />0.00201 weeks <br />4.630685e-4 months <br />, Technical Specifications (TS) 3.6.6, "Containment Spray and Cooling Systems," Condition C was entered for the 1A VP train and mechanics proceeded to remove the 1A RCFC plenum access panel. At approximately 1234 hours0.0143 days <br />0.343 hours <br />0.00204 weeks <br />4.69537e-4 months <br />, during the inspection for the leak, an interior access panel (4 by 6 feet) was discovered not installed, as required. The panel was tied off to an adjacent panel. The Shift supervisor was immediately notified. The condition was entered into the corrective action program and the 1A VP train remained in TS 3.6.6 Condition C pending resolution. The interior panel and plenum access panels were replaced and TS 3.6.6 Condition C exited at 1308 hours0.0151 days <br />0.363 hours <br />0.00216 weeks <br />4.97694e-4 months <br /> on March 29, 2012.
The function of this interior panel is to ensure all containment air is directed across the SX coils for cooling. During accident conditions, when WO cooling is lost to the WO coils, this opening would allow some of the air to bypass the SX coils over to the WO coils and, consequently, not be cooled.
An investigation revealed the interior panel was removed on March 15, 2011 for maintenance, during Unit 1's spring 2011 refueling outage, and inadvertently not re-installed on April 15, 2011, after maintenance completion. Due to the existence of this bypass flow path, the 1A RCFC was considered inoperable when interior panel was not installed.
The 1A VP train was inoperable for longer than allowed by TS 3.6.6 Condition C and Limiting Condition for Operations (LCO) 3.0.4 was initially inadvertently violated at 0315 hours0.00365 days <br />0.0875 hours <br />5.208333e-4 weeks <br />1.198575e-4 months <br /> on April 21, 2011, when Unit 1 entered Mode 4 in returning to power after the spring 2011 refueling outage and after returning to power after a March 2012 maintenance outage. Therefore, this event is reportable to the NRC in accordance with 10CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS. In addition, the 1B VP train was also taken inoperable for maintenance on four occasions during this time period for approximately 30 collective hours which also makes it reportable to the NRC in accordance with 10 CFR 50.73 (a)(2)(v)(B) as an event or condition that could have prevented fulfillment of a safety function.
C. Causes of the Event The cause was determined to be an inadequate level of details in the work package for the March 15, 2011, removal of the 1A RCFC panels. The work package generically stated to remove panels and did not specifically identify each panel to be removed and reinstalled. A separate work crew re-installing the panels on April 19, 2011, did not recognize the interior panel was removed and, therefore only re-installed the plenum access panel.
Contributing causes include insufficient drawing details concerning the panels in terms of number of panels and locations and the panels not having unique equipment identifier.
D. Safety Significance
There were no actual safety consequences as a result of the diminished cooling capacity of the 1A VP train. The 1B VP train was operable during this period except for four occasions; on August 31, 2011, for approximately 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />, December 29, 2011 for approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, March 29, 2012 for 26 minutes and March 29, 2012 for 33 minutes. During these periods both Unit 1 CS trains were operable.
E. Corrective Actions
The remaining RCFC plenums in Unit 1 were inspected and all other internal panels were found properly installed.
Unit 2 RCFC plenums will be inspected in the next refueling outage.
The RCFC panels will be given unique equipment identifiers and each panel will be labeled accordingly.
The drawings will be revised to reflect equipment identification for the RCFC panels.
The model work package for the RCFC panel removal will be revised to include instructions for each panel to be removed and re-installed; to include their unique identification number.
F. Previous Occurrences
No previous events were identified at Byron Station in previous three years.